....I must admit that, when viewed at equivalent sizes, I can't see any difference between the small ooc JPEG and the much larger CIZ images, but the upsized RAW beats them both, with more detail, fewer artefacts and better colour. There are slightly sharper jaggies visible in diagonal lines in the RAW, but they're only just visible at 100% viewing.

So I wonder what secret sauce Sony uses in its CIZ resampling algorithm that manages to be worse than the pedestrian bicubic?

They did smooth out the jaggies, at least for the obvious lines and curves in the letters, and gave an appearance of more detail in those areas. In the RAW version, these jaggies are still present. In this area, CIZ "won".

It's just that when you looked for actual detail, such as the map shading, it was preserved in the RAW version but somehow smoothed-out in the CIZ version. It seems to me that CIZ should have at least done as well, but it did not. Perhaps this is either an artifact of the JPEG processing or a slight focus difference?

I think the color/exposure problem is unrelated to CIZ, but makes it overall less appealing. In my quick tests, the color was preserved with CIZ (same as JPEG), and using a TC introduced less contrast (along with more detail). So, there are tradeoffs, but I still see CIZ as being a convenience for someone that wants it processed all in the camera. I guess as long as CIZ beats a JPEG crop, it is still useful for JPEG users.